A university warehouse has received a shipment of 25 printer

A university warehouse has received a shipment of 25 printers, of which 10 are laser printers and 15 are inkjet models. If 6 of these 25 are selected at random to be checked by particular technician, what is the probability that exactly 4 of those selected are laser printers? what is the probability that at least 5 of those selected are laser printers?

Solution

Total printers = 25

Laser = 10

Inkjet = 15

6 out of 25 are selected : 25C6

a) Probability of exaclty 4 of those laser printers :

selcting exactly 4 aser printers = 10C4

remaing 2 = 15C2

Probability of exaclty 4 of those laser printers : 10C4*21C2/25C6

= 210*105/(177100) = 0.124

b) Probability of atleast 5 of those selected laser printers:

Atleast 5 = (10C5*15C1 + 10C6 )25C6 = ( 252*15 + 210)/177100 = 0.0225